1. Field of the Invention
The present invention relates to a photonic integrated device and, more particularly, to a photonic integrated device using a reverse-mesa structure and a method for fabricating the same, which is capable of simplifying a fabricating process for the photonic integrated device while reducing serial resistance of the device.
2. Description of the Related Art
Recently, research and studies have been actively carried out for integrating various optical devices having various functions onto a substrate in order to realize a photonic integrated circuit. In particular, an amplifier and modulator integrated distributed-feedback laser diode (hereinafter, simply referred to as “AML”), in which a semiconductor laser, an optical modulator, a semiconductor optical amplifier and a photo detector are integrated onto a single substrate, has become a matter of concern and interest.
FIG. 1 is a sectional view showing a conventional AML device having a buried hetero (BH) structure. As shown, the conventional AML device includes an n-InP clad layer 1, an active layer 2, an i-n current shielding layer 3, p-InP clad layer 4, a contact layer 5, and an insulating layer 6. Generally, the p-InP clad layer 4 has a mesa structure.
The conventional AML device, although it may vary depending on the sort of current shielding layers, requires five re-growth steps that include layer growth for forming diffraction gratings, a growth for a mesa-etching, a current shielding layer growth, a p-clad layer growth. And an insulating layer growth for isolating between devices are required. While the re-growth steps are increased, a planarization degree of a surface may be lowered and a significant alignment error may occur during a photolithography process. In the case of an electro-absorption modulator integrated distributed-feedback laser (EML) or an AML device, it is required to minimize the reflection at an optical output facet, since a far field pattern (hereinafter, simply referred to as “FFP”) is significantly distorted due to an irregular surface of a window area. That is, if the total thickness of the window area is thin, a beam reflected from a surface of the window area interferes with a linear beam so that not only is a side lobe created, but also an offset phenomenon causing a peak value to be biased to 0 may occur. Therefore, it is necessary to form a p-clad layer with a relatively large thickness. However, if the thickness of the p-clad layer increases, serial resistance of the device also increases. Thus, the above structure may inevitably cause an increase of serial resistance due to the large thickness of the p-clad layer. Particularly, in the case of a device operating at a high speed above 10 Gb/s, an RF characteristic of the device may be deteriorate.